Method of refining metals



Patented Aug. 3, 1926.

1,594,424 PATENT OFFICE. i

JOHN J. MULLIGAN, OF EAST CHICAGO, INDIANA, ASSIGNOR T UNITED STATES SMELTING REFINING & MINING COMPANY, 01: PORTLAND, MAINE, A CORPORATION OF MAINE.

No Drawing.

The invention relates to refining and purifying metals and more particularly to methods involving the useor presence of caustic alkali such as caustic soda in the I 5 molten state.

' on the metal bath. The thickening mate-.

Metal refining methods have heretofore been proposed or used in which molten v,Inet-al is treated. with caustic alkali either.

alone or mixed with other reagents and in which the impurities rise with the freecaustic to the surface of the metal in the form of a more or less fluid dross which must be removed. The molten caustic is'a thin and fluid liquid which floats on the surface of the metal bath much as oil floats on water. So long as the covering of caustic is of considerable depth it may be run off without material difficulty but, as its thickness decreases, it is diflicult to run it off without running off some of the metal. It is also practically impossible tocompletely remove the caustic without removing more or less of the metal, since the last of the caustic floats on the metal bath in detached fugitive patches. The molten fluid caustic is also a disagreeable if not a dangerous product to handle since its contact with water may create an explosionwith a scattering of caustic through the air and also because its causticity intensifies a burn beyond that due to its heat.

The present invention provides for con-' rial may conveniently be an inert substance having a high melting point which will form with the molten caustic a mixture which is not fluid at the temperature used.

Materials of this character which have been successfully used include ordinary building cement, crushed fire brick, crushed lead blast furnace slag ground commercial fire clay, and sand. suflicient quantity of a material of this character is scattered over the dross preparatoryto its removal and serves to thicken the molten caustic to a pasty mass which may be readily scraped or sklmmedfrom the surface of the bath. By

METHOD OF REFINING META-LS.

Application filed-June 19, -1924. Serial No. 721,125.

the addition of an excess of the refractory materials, the scum or dross may be converted into a practically dry powdery mass which may be scraped from thesurface of the bath. 4

While possibly there may be some chemical action between the caustic and some in-.

gredient of the refractory thickening material, as, for instance, between the causticcaustic in the material used.

Theabove method of removing the caustic and drossed impurities from the molten bath'may be used 1n various methods 1nvolvmg a use of caustic whlch results 1n its presence in a fluid molten state on the surface of the bath and has been applied with marked advantage in a method of removing arsenic from antim'onial lead by treatment with caustic soda which is described and claimed in application No. 678,354, filed Nov. 22, 1923, as a continuation of application No. 579,035, filed August 1, 1922. In

this method caustic soda is added to a bath of the molten alloy at a temperature between 900 degrees and 1000 degrees F. and

is thoroughly stirred into or mixed withthe molten bath, the agitation being continued until the caustic is practically spent, and the dross or scum thus formed is then removed. ;In applying the present invention to this process, the inert stiffening material is added to the scum or dross preparator to its removal and, as above explaine mixes with or absorbs the molten caustic forming therewith and with the dross impurities, a pasty or crusty mass which may be readily removed by scraping or skimming and taking with it prac cally all the fluid caustic without danger and without removal of the metal treated. If the arsenic is removed by successive fractional additions of caustic soda, the addition of the 'refractory thickening material may be omitted until the final treatment and removal of the final skim, since the presence of free caustics on the surface of the bath after eachfof the preliminaryskims will not be detrimental.

The term caustic alkali reagent is intended to include a reagent com risin caustic alkali 'either alone or mixed with other reagents.

What is claimed is':

1. Inn method of refining metals which consists in subjecting molten metal to treatment with a caustic alkali reagent to dross the impurities therein, the addition to the floating dross preparatory to its removal of a material which thickens the fluid caustic therein.

2. In a .method of refining metals comprising subjecting molten metal to treatment with a caustic alkali reagent to dross the impurities therein, adding to the floating' dross an inert material to thicken the molten caustic therein, and removing the non-fluid mixture thus formed.

3. The method of removing molten caustie and drossedimpurities from-the surface of a molten metal which consists in absorbing the fluid caustic by the addition of a thickening material and removing the nonfiuid mixture thus formed.

4 The method of removing arsenic from antimonial .lead which consists in treating the molten metal with caustic soda to dross the arsenic, adding to the dross a material JOHN J. MULLIGAN. 

